The invention relates to a control system for a clutch of the transmission, which may be a gear box or hydrostatic transmission, in a motor vehicle and more particularly in a commercial vehicle, comprising wheel tachometer sensors, a tachometer sensor at the output of the transmission and the associated tachometer magnetic elements and the electronic control system, possibly in connection with a conventional anti-wheel lock or anti-skid system.
Conventional control systems are adapted to operate in conjunction with the speed of rotation of the engine, with the input and output speeds of the transmission, and the displacement of the mechanism for the operation of the clutch and the gear selection. Furthermore the electronic system stores the rear axle transmission ratio and the tire size in its program. This is generally sufficient in the case of private cars with small variations in the overall weight for the determination of the clutch operation time.
However, the picture is different in the case of commercial vehicles such as buses with great variations in weight between the vehicle in the fully loaded and unloaded conditions. Furthermore a vehicle may be adapted for use on roads and cross country and this involves different wheelbases and lengths of the drive train, axle transmission ratios and tire sizes. In the case of large differences in torque the driver is often no longer able to operate the clutch smoothly while still ensuring a short slip time. The shorter the slip times, particularly on hills, the shorter the interruption in the tractive effort and therefore the loss of speed during changing gear. However, in the case of empty vehicles traveling on a flat road the time taken to engage the clutch should not be too short for reasons of comfort, since owing to a reduced mass of the vehicle, changing gear then causes jerks which are unpleasant.
In order to solve such problems it would prima facie be possible to arrange load sensors on all axles or, respectively, all wheels and to evaluate the readings from the sensors in combination with the readings from a sensor responding to the road inclination. However, a more detailed consideration will show that this system would be very complex and therefore high in price. In order to measure the state of loading of the entire vehicle, each axle would have to be fitted with a sensor, that is to say including the axles of any trailer. This would however mean that the electronic control system would still not be informed whether the vehicle was to be accelerated or braked or is only to coast along. Furthermore it is not possible to detect whether the road is in a smooth or rough, condition.